Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $143.91   13.240%   $162.9637   $162.96   $162.95   $163.00  
  Purchase #2 $90.88   7.779%   $97.9496   $97.95   $97.95   $97.90  
  Purchase #3 $210.61   11.677%   $235.2029   $235.20   $235.20   $235.20  
  Purchase #4 $45.53   12.165%   $51.0687   $51.07   $51.05   $51.10  
  Purchase #5 $22.81   9.105%   $24.8869   $24.89   $24.90   $24.90  
  Purchase #6 $98.31   9.872%   $108.0152   $108.02   $108.00   $108.00  
  Purchase #7 $172.96   9.234%   $188.9311   $188.93   $188.95   $188.90  
  7 purchase totals = $785.01       $869.0181   $869.02   $869.00   $869.00